I also like the Payette paste made by Loon (Loon makes some pretty wonderful products in general).
I have found that when fishing dries (esp. small ones) in faster water or in back-eddies behind medium to large rocks, that if my thread leader sinks below the surface I cannot mend the line easy enough to prevent the fly from moving when I do so.
That was enough last weekend to make me miss a possible hook-up. I had a fly sitting right behind a rock in some still water with water rushing past on both sides. I had to mend the line when the leader fully extended in the current, but with the leader slightly underwater, the fly moved just as a fish came to look at it and he turned away. However, it is almost effortless to mend the line when the leader is floating high on the water, and it is easy to do so without moving the fly.
"Engineers don't idle well."